##  [The Prado Wetlands: 24 Years of River Diversion Treatment Wetlands Reducing Nitrate and Phosphate while Increasing an Endangered Bird](/resource/prado-wetlands-24-years-river-diversion-treatment-wetlands-reducing-nitrate-and-phosphate) 

Organization

[University of California](/organization/university-california)

 

 

Resource Type

[Peer reviewed article](/taxonomy/term/37)

 

 

Author(s)

Alex Horne

Marc Beutel

Greg Woodside

 

 

Original Authors

Alex Horne

Marc Beutel

Greg Woodside

 

 

Contacts

[Alex Horne](/contact/alex-horne)

 

 

Resource Date:

2024

 

 

Nitrate pollution of [surface water](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/surface-water "Learn more about surface water from ScienceDirect's AI-generated Topic Pages") from farms and [urban runoff](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/urban-runoff "Learn more about urban runoff from ScienceDirect's AI-generated Topic Pages") is widespread – impairing [drinking water supplies](https://www.sciencedirect.com/topics/earth-and-planetary-sciences/drinking-water-supply "Learn more about drinking water supplies from ScienceDirect's AI-generated Topic Pages"), recreation, and wildlife habitat. The scale of the problem in rivers has overwhelmed most watershed-based [best management practices](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/best-management-practice "Learn more about best management practices from ScienceDirect's AI-generated Topic Pages"). A new paradigm is needed. In this paper we highlight the 119 ha (294 acres) Prado Wetlands in southern California, [USA](https://www.sciencedirect.com/topics/earth-and-planetary-sciences/united-states-of-america "Learn more about USA from ScienceDirect's AI-generated Topic Pages") as an example of a gravity-enabled, free surface flow vegetated wetlands to treat a river – the nitrate-rich, effluent-dominated Santa Anna River. The wetland treats ∼1–2 m3/s of the 7.1 m3/s (250 cfs) flow of the river in 28 wetland cells in two parallel trains (residence time 2–4 d, hydraulic loading rate 10–20 cm/d). The cleaner water is returned to the river and infiltrated downstream into a managed groundwater basin supplying 2.4 million customers. Since 1998, ∼1200 t of nitrate-N have been permanently removed from the river and released as N2-gas into the air. Over 24 years, in the warm summers an average of 6.1 mg-N/L entered the wetland and 3.7 mg-N/L flowed out, a removal efficiency of 57%. In the cooler winters, an average of 6.4 mg NO3-N/L entered and 2.6 mg NO3-N/L flowed out, a removal efficiency of 45%. Individual months varied widely in concentration removal efficiency from 7% (winter) to 98% (high summer). Areal summer removal averaged 137 mg NO3-N/m2/d and the apparent “k” was around 46 m/y. All-year rates were 129 mg NO3-N/m2/d or 47 g/m2/y, a reasonable performance considering the size of the system and its configuration for both nitrate removal and duck hunting (i.e., more open water). Annual average nitrate removal efficiency increased substantially over time (45 to 72% for 1998–2004 versus 2016–22) and is attributed to an increase in hydraulic residence time, upgraded internal plumbing, and increased winter temperatures (+3C°). Prado Wetlands also removes phosphorus, though not as well as nitrate; average warm season removal efficiency was 23% (inflow 1.20 mg PO4-P/L, outflow 0.93 mg PO4-P/L). The aerial removal rate was high at 23 mg P/m2/d or 8.5 g/y, probably due to the high inflowing P-concentrations and the hard water. Wildlife was also enhanced. Least Bell's Vireo (*Vireo* [belli](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/bellis "Learn more about belli from ScienceDirect's AI-generated Topic Pages") *pusillus)*, an endangered bird in the Prado Basin, increased from 19 pairs (1998) to a recent average of 444 pairs due to habitat improvement and reduction of [cowbird](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/cowbird "Learn more about cowbird from ScienceDirect's AI-generated Topic Pages") parasitism. Results from the Prado Wetlands show that cleaning up rivers via diversion through wetlands benefits both water quality and wildlife.